This invention relates generally to inspection techniques, and more specifically to methods and apparatus for inspecting components.
Accurately measuring a surface of a component may be a significant factor in determining a manufacturing time of the component, as well in determining subsequent maintenance and repair costs and activities. Specifically, when the component is a gas turbine engine shroud, accurately measuring the contour of the shroud may be one of the most significant factors affecting an overall cost of fabrication of the gas turbine engine, as well as subsequent modifications, repairs, and inspections of the blade airfoils. For example, at least some known gas turbine engine shroud segments are small and include a snubber section and a racetrack section. For performance reasons, both the snubber section and the racetrack section require an accurately machined thickness. However, accurately measuring the thickness of the snubber and racetrack sections may be difficult because of the relative small size of the shroud segment.
At least some known inspection processes use coordinate measuring machines (CMMS) or other gages to obtain dimensional information for a shroud segment. Within at least some CMMs and gages, the thickness of a section of a shroud segment is determined by measuring a drop from a surface of the shroud segment to a surface whose location is known, such as a fixture used with the CMM or other gage. However, determining the thickness of a section of a shroud segment by measuring the drop to a known surface does not directly measure the thickness of the shroud segment, and therefore may be inaccurate. Furthermore, at least some known shroud segments must be removed from the machining apparatus prior to being inspected by a CMM or other gage. Removing the shroud segment from a machining apparatus increases the number of fabrication operations and the number of apparatuses used for manufacturing, thus increasing manufacturing time and cost. In addition, if the shroud segment fails the inspection, the segment may then need to be reinstalled in the machining apparatus for further machining. However, because of the size and contour of the shroud segment, it may be difficult to reinstall the shroud segment within the machining apparatus in the same relative position with respect to the original machining, thereby increasing error and manufacturing time.